If you want to learn how to use XOS (and don't have access to any extreme networks switches) it'll come in handy. I haven't tested all the features from the User Manual, since some of the hardware dependent features probably don't work, but it'll be enough to get your feet wet.

just as a heads up, the good people at Extreme are considering adding a pre-made .qcow2 Qemu file, to make it easier to integrate into GNS3. They also have instructions for installing EXOS as Virtualbox and VMwaew VMs.